The experiments proposed in this grant application will examine postulates regarding the information processing occurring in the cerebellum during the learning of motor behaviors. These studies will be among the first to employ multiple single unit recording techniques to characterize the learning-related modulation of small populations of neurons simultaneously in both the cortex and nuclei of the cerebellum during the acquisition of three motor tasks: the classically conditioned eye blink in the rabbit and cat, the classically conditioned forelimb withdrawal reflex in the cat, and an instructed delay reaching paradigm, also in the cat. Each of these learned behaviors is dependent on an identified region of the cerebellum. These experiments will use three different paradigms, each requiring a different type of short-term memory process for its performance. In the first of these, the delay paradigm for conditioning the eye blink and withdrawal reflexes, the appropriate timing of the learned behavior is dependent upon the retention of the interval between the conditioned and unconditioned stimuli, an interval which is cued every trial in this paradigm by the duration of the conditioned stimulus. In the second, the trace conditioning of the same reflexes, the interstimulus interval again must be retained, but the interval is not cued on successive trails. Consequently, the proper timing of the conditioned behavior is dependent on an internal representation of the interstimulus interval that is not reinforced by the duration of the CS. The third paradigm, an instructed delay paradigm, employs an operantly conditioned task in which the performance of a reaching movement is dependent upon retaining the target's location for a brief period before the reach is initiated. The changes in information processing occurring simultaneously in functionally related regions of the cerebellar cortex and nuclei during the acquisition of each of these tasks will be examined to test specific hypotheses pertaining to (1) the early modification of neuronal responses preceding the appearance of the conditioned behavior, (2) the action of the climbing fiber system during task acquisition, and (3) the relationship between the learning-related modulation in the cerebellar cortex and that occurring in the cerebellar nuclei. The data processing will assess the relationships among the modulation of the simple spike activity of Purkinje cells, the activation of their climbing fiber inputs, the discharge of cerebellar nuclear neurons, and the characteristics of the conditioned behavior at specific stages of the acquisition process. Because of the unique interrelationships among the paradigms employed in these experiments, the findings not only will elucidate those aspects of information processing that are specific to the learning of each task, but they also will reveal those features which are generalizable across these behaviors.